I am now considering the combo approach with a lowrider rack and a handlebar bag (or possibly a minirack). I just found the Arkel AC Lowrider (Used to be sold by OMM?) which looks like it might be a nice compromise with a few extra inches of ground clearance than most other lowriders including Tubus. Bonus is that I can order it at the same time as my Arkel panniers!
That Arkel looks like it offers a lot of adjustability, which is good because when your mounts are not like the ones on all other bikes, that can be important. It looks like you only have one position for the low rider, but that is not a problem either.
A handlebar bag and small platform can work together, but the handlebar bag clearly can limit how much you get on the rack. In this photo I have my rain jacket on the rack under my handlebar bag. This is the Sunlight (or maybe Sunlite?) rack, not the Nashbar one.
If you mount a handlebar bag, note how I used a second stem to lower it.